Apparatus for drying finely divided materials while suspended in a gas



g- Tlg,

Dec. 21, 1948; CAUGHEY 2,456,674

APPARATUS FOR DRYING FINE-LY DIVIDED MATERIALS WHILE susrmman In A GAS Filed D00. 12, 1945 IIIJI III/Ir Clttomega.

5/ 2 I I hunter:

- heated air stream tends 'sary if suilicient time is Patented Dec. 21, 1948 APPARATUS FOR DRYING FINELY DIVIDED MATERIALS WHILE SUSPENDED IN A GAS Robert A. Caughey, Wilton, N. H. Application December 12, 1945, Serial No. 834.417

11 Claims.

The present invention relates to a method of and apparatus for the rapid and eiflcient drying of finely divided low density materials, such as wood shavings, sawdust. ground leather, etc. Most materials of this general character are produced in such a manner that the particle size is widely variable and, consequently, require diiferent drying periods to produce a uniformly dried product.

In the conventional dryer, the material to be dried is fed into one end of a rotary cylinder and gradually works its way toward the other end where it is discharged in the dry condition. The drying medium usually is heated air which is fed into the drying cylinder at the discharge end and passes through the dryer countercurrent to the flow of the material to be dried. In drying very light materials, it has been found that the to carry the finer particles back towards the feed end. Consequently, the fine particles remain in the dryer longer than the larger particles and longer than is necesallowed for complete drying of'the coarser particles. In either case,

the product is not uniformly dried. If it is attempted to increase the drying rate by increasing the volume and velocity of the heated air, the tendency for the finer particles to be blown out of the dryer is increased. These conditions result in a relatively low heat eiilciency and necessitate the use of special equipment for removal of the fine particles.

In accordance with the present invention, the particles of the material to be dried are classified during th process of drying in such a manner that the particles are retained in the drying chamber for a period of, time substantially proportional to their mass and to the sired degree of drying. particles, which .can be pass through the drying period of time than the coarse and heavy particles. A uniformly dry product is obtained with a minimum expenditure of heat.

Thu -thefine'aifidlight fig more rapidly. will chamber in a shorter the lower end of a hopper 20 time required for the d e=.

The invention will be more clearly understood 7 from the following description in conjunction with the accompanying drawings, in which:

Fig. 1 is an elevational longitudinal view, partly in section, of an apparatus embodying the invention;

Fig. 2 is a sectional view taken upon the line 2-2 of Fig. 1;

Fig. 3 is a sectional view taken on the lines 3-3 of Figs. 1 and 2; and

Fig. 4 is a fragmentary plan view of a portion of the apparatus.

As illustrated in the accompanying drawing, an apparatus embodying the invention may comprise a drying chamber Ill having a substantially cylindrical wall ll, preferably, positioned with its axis substantially horizontal. The ends 8 and 9 of the wall il overlap slightly and are spaced slightly from one another as shown in Fig. 2 to provide a passage I! into the interior of the drying chamber it for a purpose described, hereinafter. A plenum chamber l3 extends longitudinally along the cylindrical wall II and comprises a bottom wall It and a side wall Ill. The free end of the side wall it is secured to the outer surface of the .9 of the cylindrical wall Ii, as by welding. The

ends of the cylindrical wall the plenum chamber it are and I1. One end of a tube 2| ii and the ends of closed by plates l8 communicates with and the other end of the tube communicates with the interior of the drying chamber Ill through the plate It. A feed screw 22 is positioned in the tube 2| and is adapted to feed finely divided material from the hopper 20 into the drying chamber i 0. The shaft of the feed screw 22 projects through the wall of the hopper 20 and carries a pulley 23. The armature shaft of a motor 24 is provided with a pulley 2! which is operatively connected to the pulley 23 by a belt 26.

The intake passage of a blower 30 communicates with a source (not shown) of heated air or other heated gaseous drying medium which is inert toward the material to be dried. The outlet v f the.blowersloeommunicates with the interior sure and is introduced tangentially into the drying chamber In through the longitudinally extending passage or orifice l2 at a velocity greater than is necessary to maintain the finely divided material to be. dried in suspension. One end of a tubular passage 35 provides communication through the end plate i1 with the interior of the drying chamber ill and the other end of the tube 35 communicates withthe intake of an exhaust fan or blower 38. The exhaust fan 35 communicates through a tubular separator 38. The orifice l2, preferably, is located along the lowest portion of the drying chamber ll.

A plurality of stationary bellies 40 are positioned passage 31 with a cyclone within the drying chamber adjacent the orifice i2 and are inclined from the orifice back toward the feed end of the drying chamber for a purpose explained hereinafter. One end of each of the bailles 40 is pivotly carried by a bolt 4| secured to a rod 42 extending longitudinally within the drying chamber and secured to the end walls 16 and IT by a nut 43 threaded upon each end thereof and engaging the end walls 16 and I1. Each bolt 4! passes through top and bottom flanges 3 and 4 respectively of the baifles 40. A washer 2 surrounding each bolt 4|. serves as a spacing block between the overlapping ends 8 and 9. Nuts 39 and 44 threaded -on each bolt 4| engage the top baflle secured to the overlapping'end 9. The other end of each baflle is pivotally carried by rivets 48 extending between the top 'baifle flange 3 and a rod which extends longitudinally through the dry chamber parallel to the rod 42. The rod 45 is mounted in the end walls It and I1 in any flange 3 and the wall I4 A terial having particles requiring diflerent drying suitable manner for longitudinal movement relative thereto whereby the inclination of the bafiles 40 may be adjusted in synchronism.

In the operation of the apparatus, a heated gaseous drying medium is forced by the blower 30 into the plenum chamber l3 under sufllcient pressure so that it will pass through the orifice i2 at a velocity approximately twice that neces sary for the suspension of the coarser particles to be dried. The capacity of the exhaust fan 36. preferably. is slightly greater than that of the blower 30 so that the pressure within the drying chamber is slightly lower than that outside. The fan 36 withdraws air and the dried particles sus pended therein and forces it through the passage 31 to the cyclone separator 38. The motor 24 causes the feed screw 22 to rotate and thus feed finely divided material to be dried from the hopper 20 intothe drying chamber |0.- As the stream of air passes through the orifice I2 it tends to move in a circular path at relatively high velocity adjacent the cylindrical wall of the drying chamber and carries the finely divided material in suspension. However, since the exhaust fan 36 operates to withdraw air from the drying chamber as fast as it enters, the air-containing suspended particles to be dried tends to move in a spiral path from the feed end of the drying chamber to the discharge end thereof. During this travel of the suspended particles they are periodically and successively brought in engagement with the baflies 40 which act as deflectors deflect them back toward the feed end of the drying chamber. Since the angle of deflection of the particles will be the same and the carrying capacity of the heated air is proportional to'the mass of the particles, the larger or heavier particles will be deflected a greater distance back to- V wards the feed end of the drying chamber than the'finer particles.

The finer particles will be more quickly divertednby the air stream back into the normal stream of travelandwLll pass through the drying apparatus at a more rapidrate. It will be apparent particles are retained in the drying chamber will be substantially proportional to their mass and to the actual time required to dry them to the same moisture content and can be controlled by adjusting the angle of the baflies 40. By' the practice of the invention, a final dried product is obtained in which all the particles 'have been dried to substantially the same moisture content.

I claim: v 1. An apparatus for drying finely divided'mathat the time which the various periods drical wall and end walls forming a drylngchamber, means for introducing a stream of heated air tangentially to the cross section of the said cylindrical wall into the drying chamber at a velocity greater than that required to maintain said materlal in suspension and for withdrawing air from near one end of the drying chamber and tending to move said heated air in a helical path through said chamber, means for feeding said material into said helically moving stream near the other end of said chamber, and stationary means for successively deflecting said suspended material back away from the withdrawal end of said chamber and against the general direction of movement of the air in said chamber.

2. An apparatus for drying finely divided material having particles requiring different drying periods which comprises a substantially cylindrical wall and end walls forming a drying chamber, means for introducing a stream of heated air into the drying chamber tangentially to the cross section of said cylindrical wall forming an entrance orifice extending substantially its entire length at a velocity greater than that required to maintain said material in suspension and for withdrawing air near one end of the drying chamber and tending to move said heated air in a helical path through said chamber, means for feeding said material into said helically moving stream near the other end of said chamber, and stationary means positioned adjacent the wall of the drying chamber for successively deflecting said suspended material back away from the withdrawal end of said chamber and against the general direction of movement of the air in said chamber.

3. An apparatus for drying finely divided ma-' terial having particles requiring different drying which comprises a substantially cylin- V periods which comprises a substantially cylin-- drical wall and end walls forming a drying chamber, meansfor introducing a'stream of heated air tangentiallyto' the cylinder formed by said cylindrical wall into the drying chamber at a velocity greater than that required to maintain said material in suspension and for withdrawing air from near one end of the drying chamber thereby tending to move said heated air in a helical path through said chamber, means for feeding said material into said helically moving stream near the other end of said chamber, sta,-- tionary means for successively deflecting said suspended material back away from the withdrawal end of said chamber against the general direction of movement of air in said chamber, and means controlling the distance which said suspended material is deflected back.

4. An apparatus for drying finely divided material having particles requiring different drying periods which comprises a substantially cylindrical .wall and end walls forming a drying chamber, means for introducing a stream of heated air tangentially tothe cylinder formed by said cylindrical wall into the drying chamber oughout substantially its. entire'length at a velocitygreater than that required to maintain said material in suspension and for withdrawin air from near theopposite end of the dryin chamber thereby tending to move said heated air in a helical path through said chamber, means forfee'ding said material into said elically moving stream near the other end of said chamber,

stationary means positioned adjacent the wall of the drying chamber for successively deflecting stantially its entire length into said suspended material back away from the withdrawal end 01' said chamber againstthe general direction 01' movement of the air in said chamber, said stationary means being adjustably arranged for controlling the distance which said suspended .material is deflected back.

5. An apparatus for drying finely divided main a helical path through said chamber, means for feeding said material into said helically moving stream near the other end of said chamber and longitudinally spaced stationary baiiies positioned adjacent the wall of the drying chamber for successively deflecting said suspended material back away from the withdrawal end of said chamber and against the general direction of movement of the air in said chamber.

8. An apparatus for drying finely divided material having particles requiring difierent drying periods which comprises a substantially cylindri cal wall and end walls forming a drying chamber, means for introducing a stream of heated air tangentially to the cylinder formed by said cylindrical wall forming an entrance into the drying chamber throughout substantially its entire length at a velocity greater than that required to maintain said material in suspension and for withdrawing air from near one end of the drying chamber thereby tending to move said heated air in a helical path through said chamber, means for feeding said material into said helically moving stream near the other end of said chamber and longitudinally spaced stationary bafiles positioned adjacent the wall of the drying chamber and adjacent the region said air stream enters the drying chamber for successively deflecting said suspended material back away from the withdrawal end oi said chamber, the drying chamber being positioned substantially horizontal and the entrance for said air stream into the drying chamber being substantially along the'lowest region of the drying chamber.

7. An apparatus for drying finely divided material having particles requiring difi'erent drying periods which comprises a substantially cylindrical wall and end walls forming a drying chamber, means for introducing a stream of heated air tangentially to the cylinder formed by said cylindrical wall forming an entrance into the drying chamber throughout substantially its entire length at a velocity greater than that re- 8. An apparatus for drying finely divided material having particles requiring difierent drying periods which comprises a substantially cylindrical wall and end walls'iorming a drying chamber, means ,ior introducing a stream qi' heated air tangentially to the cylinder formed by said cylindrical wall forming an entrance into the drying chamber throughout substantially its entire length at a velocity greater than that required to maintain said material in suspension and for withdrawing air from near one end of the drying chamber thereby tending to move said heated air in a helical path through said chamber, means for feeding said material into said helically moving stream, longitudinally spaced bailles positioned adjacent the wall of the drying chamber and adjacent the region said air stream enters the drying chamber for successively defiecting said suspended material back away from the withdrawal end 01' said chamber against the general direction ot'movement oi the air in said .chamber, and means for adjusting the inclination 01 said baiiles, the drying chamber being positioned substantially horizontal and the entrance for said air stream into the drying chamber being substantially along the lowest region oi quired to maintain said material in suspension lengthwise oi the drying chamber.

9. An apparatus for drying finely divided material having particles requiring diilerent drying periods which comprises a cylindrical drying chamber, a plenum chamber-extending substantially the entire length of the drying chamber and having a substantially coextensive orifice for introducing a stream of air tangentially into the cylindrical drying chamber, means for introducing heated air under pressure into the plenum chamber, means for withdrawing air from the opposite end of the drying chamber whereby said stream 01' heated air tends to move in a spiral path through the drying chamber, means for feeding the finely divided material into said spirally moving stream, and longitudinally spaced baiiies positioned adjacent the wall or the drying chamber and said orifice and inclined to defiect said suspended material back away from the withdrawal end of the drying chamber.

10. An apparatus for drying finely divided material having particles requiring diilerent drying periods including a longitudinal substantially cylindrical wall and end walls forming a drying chamber longitudinally through which the material travels during drying, a plenum chamber extending the length of the drying chamber and connected therewith by means forming a continuous tangential entrance orifice for the passage 01' gas into said chamber, said drying chamber having means forming a feed entrance for the material at one end and means forming an exit orifice for said material and gas at the end opposite the entrance and stationary deflectors within the drying chamber and distributed it arranged to return the heavier particles toward the entrance end.

11. An apparatus for drying finely divided material having particles requiring difi'erent dry-v ing periods including a longitudinal substantially cylindrical wall and end walls forming a drying chamber longitudinally through which the material travels during drying, a plenum chamber ex tending the length of the drying chamber and connected therewith by means forming a continuous tangential orifice for the passage oi gas into said chamber, said drying chamber having means forming a feed entrance for the material at one end and means iorming an exit orifice tioles toward the entrance end. ROBERT A. CAUGHEY REFERENCES CITED The following references are of record in the me of this patent:

UNITED STATES PATENTS Name Date Number Christensen Jan. 22, 1935 Number 10 Number Q Name Date Fenby Dec. 3, 1935 Otis -4. Jam-28, 1936 'Peebles May 11, 1937 McGehee et a1. Nov. 30, 1937 Bar June 13, 1944 Arnold Feb. 19, 1946 I' OREIGN PATENTS Country Date Great Britain Apr. 8, 1935 Great-Britain June 26, 1942 

